It's not quite the Manhattan Project or Area 51, but the Swiss take their cheese very seriously and want to protect the trade secrets that make their cheeses famous and sought after around the world.
As a consequence, Tom Scott wasn't able to see all or possibly even most of the Agroscope facility. But he was able to pry out of the food scientists why Swiss cheese has (or at least used to have) many holes inside. It's not because of the traditional explanation: bubbles of carbon dioxide formed during the fermentation process.
The Swiss scientists were able to discover the reason why their cheese were gradually become less hole-y about thirty years ago. In short, the milk was too clean and a certain contaminant wasn't getting into the milk and flavoring the resulting cheese. Now that particular contaminant has not be added in intentionally.